Hitherto, a gap between members formed in constructs such as buildings, vehicles, electronic devices is filled with a sealing material, to provide water cut-off, heat insulation and sound absorption. Foams made of synthetic resins or rubbers are used for the sealing materials. The foams have appropriate repulsive force (compression stress). Therefore, the foams adhere, due to compliance, to the irregularity on the surface of the members to be sealed, under application of small compression deformation. Accordingly, an excellent seal property can be attained.
Above all, a rubber foam obtained by expanding ethylene-α-olefin-diene copolymer rubber foam by using a blowing agent such as azodicarboxylic acid amide is preferably used as a sealing material, because of excellent weather resistance, heat resistance and seal properties (Patent Literature 1 and 2). In the rubber foam, the smaller the cell diameter or the higher the cell density, the more improved the properties required by the foam (water cut-off property, heat insulation property, sound absorption property, etc). Therefore, the rubber foam is subjected to bubble control by use of a cell diameter control agent such as stearic acid.
The rubber foam prepared by use of a blowing agent mainly includes a closed cell structure. Therefore, the foam tends to have low dimensional stability and flexibility, and sometimes does not have sufficient seal properties. As a countermeasure, the closed-cells in the rubber foam are broken in accordance with cell breakage treatment such as roll crush and vacuum crush, to produce a rubber foam having open-cell structure.